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In any discussion of the Pacific War, sooner or later it turns into a discussion of just what might have happened had the largest Japanese battleship, HIJMS Yamato had met the largest USN battleship, USS Iowa in a toe-to-toe fight.

First, the basic stats:

Yamato had a full load displacement of 69,888 tons (she was the largest warship ever launched until the nuclear-powered USS Enterprise in the 1960s). Her length at the waterline was 839'11" with an overall length of 862'9". Beam was 121'1" and she had a draft of 34'1".

Iowa's full load displacement was 57,540 tons. Her length at the waterline was 860" with an overall length of 887"3". She had a beam of 108'2" and a draft of 36'3".

The key features here are the beam and draft measurements, typically a wide-beamed ship with deep draft is a steadier gunnery platform. Yamato being wider and Iowa being deeper, both balance out in the long run. Iowa had a better layour of rudders vs Yamato and actually had a smaller tactical diameter (this is the minimum diameter necessary to make a full circle), thus making her more maneuverable.

Machinery wise, Yamato had twelve boilers and four sets of turbines giving her a max shaft horsepower of 150,000 and a maximum speed of 27 knots. The Iowa had eight boilers and four sets of turbines which turned out 212,000 shaft horsepower with a sustained speed of 32.5 knots (the Iowas were able to reach 35 knots during trials for short periods).

Iowa's higher sustained speed gave her the advantage in closing the range and her ability to kick up to 35 knots whould have given Yamato problems in tracking.

Yamato's armor protection was: Her main belt was 16.1"; her deck armor was 9"; her barbettes (turret bases) was 21.5"; the turret faces had 25.6"; and her conning tower had 19.7" of protection. Iowa had a belt 12.9" thick; deck armor 8.1"; barbette: 17.3"; turret faces of 19.7" and conning tower of 17.5".

On paper, at least Yamato had the advantage, but this is rather deceptive. Thickness of plate also has to make an allowance for quality. In the years prior to WWII, the USN had made considerable strides in armor technology, as a result, the protection offered by its new armor plate was equivalent to about 25% more thickness than the old type of armor used by Yamato. Iowa also appears to have been much better constructed than Yamato. On December 25, 1944, Yamato took a single torpedo hit that demonstrated that the jointing in between her armor belt and her hull was faulty. To correct the fault, the IJN concluded that it would have to add an additional 5,000 tons worth of bracing and armor to the ship's displacement. The IJN simply repaired the hole and pretended that there was no problem.

Armament wise, the Yamato mounted three triple turrets mounting 18.11-inch/45 rifles (two forward and one aft), a secondary armament of two triple 6.1-inch/60 rifles (one each fore and aft), and a dual purpose armament of twelve twin 5-inch/40 rifles. Iowa mounted three triple turrets mounting 16-inch/50 rifles and a dual purpose armament of ten twin 5-inch/38 rifles.

So just how good were the main armament? The 18.11-inch naval rifle had a muzzle velocity of 2,550fps. It could fire one round per gun per minute. The 16-inch rifle had a muzzle velocity of 2,560fps and a rate of fire of two rounds per gun per minute.

At first glance, the 18-inch gun fires a shell weighing some 20% more than the 16-inch, and has a 7% greater range.

But the American advantage is a bit more subtle. The 16-inch had a longer barrel length than the 18-inch, this gives the shell more stability in flight, giving it greater range.

Its when the penetration capability of the two guns is compared that it becomes intresting: At a range of 0 yards, the 18-incher has a pen of 34", compared to 32.62" for the 16-inch. At a range of 20,000 yards, the 18-inch will penetrate about 20.4"; at the same range the 16-inch will penetrate 20.04". Open the range to 30,000 yards and the 18-inch will penetrate about 14.7" and the 16-inch will penetrate 14.97".

But it all boils down to the fact that extended range gunnery duels did not happen. The longest-range deliberate hit by any battleship in either the First World War or in the Second was made by HMS Warspite when it scored a hot at 26,000 yards.

There is also one other factor to consider. The USN's gunnery was supported by superior fire control radar as well as better ballistic computers.

There is no doubt that in a one for one engagement, the Iowa would have emerged bloody, but victorious.